1 List of United States cities by population. ^ 2  Population projection is that of the entity known since 2016 as Ciudad de MÃ©xico and previously as the Distrito Federal. ^  Population estimate is that of the Toronto census division, which consists solely of the City of Toronto.
Lens (optics) For other uses, see Lens. A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (elements), usually arranged along a common axis.
Noun. 1. lens-a transparent optical device used to converge or diverge transmitted light and to form images. lens system, lense. anastigmat-compound lens or lens system designed to be free of astigmatism and able to form approximately point images.. a doubly convex, transparent body in the eye, behind the pupil, that focuses incident light on the retina. 5. a body of rock or ore that is thick in the middle and thinner toward the edges, similar in shape to a biconvex lens.